diff options
Diffstat (limited to 'src/backend/executor/execMain.c')
| -rw-r--r-- | src/backend/executor/execMain.c | 289 |
1 files changed, 16 insertions, 273 deletions
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c index 63a34760eec..018e9912e94 100644 --- a/src/backend/executor/execMain.c +++ b/src/backend/executor/execMain.c @@ -2417,27 +2417,29 @@ ExecBuildAuxRowMark(ExecRowMark *erm, List *targetlist) /* - * Check a modified tuple to see if we want to process its updated version - * under READ COMMITTED rules. + * Check the updated version of a tuple to see if we want to process it under + * READ COMMITTED rules. * * estate - outer executor state data * epqstate - state for EvalPlanQual rechecking * relation - table containing tuple * rti - rangetable index of table containing tuple - * lockmode - requested tuple lock mode - * *tid - t_ctid from the outdated tuple (ie, next updated version) - * priorXmax - t_xmax from the outdated tuple + * inputslot - tuple for processing - this can be the slot from + * EvalPlanQualSlot(), for the increased efficiency. * - * *tid is also an output parameter: it's modified to hold the TID of the - * latest version of the tuple (note this may be changed even on failure) + * This tests whether the tuple in inputslot still matches the relvant + * quals. For that result to be useful, typically the input tuple has to be + * last row version (otherwise the result isn't particularly useful) and + * locked (otherwise the result might be out of date). That's typically + * achieved by using table_lock_tuple() with the + * TUPLE_LOCK_FLAG_FIND_LAST_VERSION flag. * * Returns a slot containing the new candidate update/delete tuple, or * NULL if we determine we shouldn't process the row. */ TupleTableSlot * EvalPlanQual(EState *estate, EPQState *epqstate, - Relation relation, Index rti, LockTupleMode lockmode, - ItemPointer tid, TransactionId priorXmax) + Relation relation, Index rti, TupleTableSlot *inputslot) { TupleTableSlot *slot; TupleTableSlot *testslot; @@ -2450,19 +2452,12 @@ EvalPlanQual(EState *estate, EPQState *epqstate, EvalPlanQualBegin(epqstate, estate); /* - * Get and lock the updated version of the row; if fail, return NULL. + * Callers will often use the EvalPlanQualSlot to store the tuple to avoid + * an unnecessary copy. */ testslot = EvalPlanQualSlot(epqstate, relation, rti); - if (!EvalPlanQualFetch(estate, relation, lockmode, LockWaitBlock, - tid, priorXmax, - testslot)) - return NULL; - - /* - * For UPDATE/DELETE we have to return tid of actual row we're executing - * PQ for. - */ - *tid = testslot->tts_tid; + if (testslot != inputslot) + ExecCopySlot(testslot, inputslot); /* * Fetch any non-locked source rows @@ -2495,258 +2490,6 @@ EvalPlanQual(EState *estate, EPQState *epqstate, } /* - * Fetch a copy of the newest version of an outdated tuple - * - * estate - executor state data - * relation - table containing tuple - * lockmode - requested tuple lock mode - * wait_policy - requested lock wait policy - * *tid - t_ctid from the outdated tuple (ie, next updated version) - * priorXmax - t_xmax from the outdated tuple - * slot - slot to store newest tuple version - * - * Returns true, with slot containing the newest tuple version, or false if we - * find that there is no newest version (ie, the row was deleted not updated). - * We also return false if the tuple is locked and the wait policy is to skip - * such tuples. - * - * If successful, we have locked the newest tuple version, so caller does not - * need to worry about it changing anymore. - */ -bool -EvalPlanQualFetch(EState *estate, Relation relation, LockTupleMode lockmode, - LockWaitPolicy wait_policy, - ItemPointer tid, TransactionId priorXmax, - TupleTableSlot *slot) -{ - HeapTupleData tuple; - SnapshotData SnapshotDirty; - - /* - * fetch target tuple - * - * Loop here to deal with updated or busy tuples - */ - InitDirtySnapshot(SnapshotDirty); - tuple.t_self = *tid; - for (;;) - { - Buffer buffer; - - if (heap_fetch(relation, &SnapshotDirty, &tuple, &buffer, true, NULL)) - { - HTSU_Result test; - HeapUpdateFailureData hufd; - - /* - * If xmin isn't what we're expecting, the slot must have been - * recycled and reused for an unrelated tuple. This implies that - * the latest version of the row was deleted, so we need do - * nothing. (Should be safe to examine xmin without getting - * buffer's content lock. We assume reading a TransactionId to be - * atomic, and Xmin never changes in an existing tuple, except to - * invalid or frozen, and neither of those can match priorXmax.) - */ - if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple.t_data), - priorXmax)) - { - ReleaseBuffer(buffer); - return false; - } - - /* otherwise xmin should not be dirty... */ - if (TransactionIdIsValid(SnapshotDirty.xmin)) - elog(ERROR, "t_xmin is uncommitted in tuple to be updated"); - - /* - * If tuple is being updated by other transaction then we have to - * wait for its commit/abort, or die trying. - */ - if (TransactionIdIsValid(SnapshotDirty.xmax)) - { - ReleaseBuffer(buffer); - switch (wait_policy) - { - case LockWaitBlock: - XactLockTableWait(SnapshotDirty.xmax, - relation, &tuple.t_self, - XLTW_FetchUpdated); - break; - case LockWaitSkip: - if (!ConditionalXactLockTableWait(SnapshotDirty.xmax)) - return false; /* skip instead of waiting */ - break; - case LockWaitError: - if (!ConditionalXactLockTableWait(SnapshotDirty.xmax)) - ereport(ERROR, - (errcode(ERRCODE_LOCK_NOT_AVAILABLE), - errmsg("could not obtain lock on row in relation \"%s\"", - RelationGetRelationName(relation)))); - break; - } - continue; /* loop back to repeat heap_fetch */ - } - - /* - * If tuple was inserted by our own transaction, we have to check - * cmin against es_output_cid: cmin >= current CID means our - * command cannot see the tuple, so we should ignore it. Otherwise - * heap_lock_tuple() will throw an error, and so would any later - * attempt to update or delete the tuple. (We need not check cmax - * because HeapTupleSatisfiesDirty will consider a tuple deleted - * by our transaction dead, regardless of cmax.) We just checked - * that priorXmax == xmin, so we can test that variable instead of - * doing HeapTupleHeaderGetXmin again. - */ - if (TransactionIdIsCurrentTransactionId(priorXmax) && - HeapTupleHeaderGetCmin(tuple.t_data) >= estate->es_output_cid) - { - ReleaseBuffer(buffer); - return false; - } - - /* - * This is a live tuple, so now try to lock it. - */ - test = heap_lock_tuple(relation, &tuple, - estate->es_output_cid, - lockmode, wait_policy, - false, &buffer, &hufd); - /* We now have two pins on the buffer, get rid of one */ - ReleaseBuffer(buffer); - - switch (test) - { - case HeapTupleSelfUpdated: - - /* - * The target tuple was already updated or deleted by the - * current command, or by a later command in the current - * transaction. We *must* ignore the tuple in the former - * case, so as to avoid the "Halloween problem" of - * repeated update attempts. In the latter case it might - * be sensible to fetch the updated tuple instead, but - * doing so would require changing heap_update and - * heap_delete to not complain about updating "invisible" - * tuples, which seems pretty scary (heap_lock_tuple will - * not complain, but few callers expect - * HeapTupleInvisible, and we're not one of them). So for - * now, treat the tuple as deleted and do not process. - */ - ReleaseBuffer(buffer); - return false; - - case HeapTupleMayBeUpdated: - /* successfully locked */ - break; - - case HeapTupleUpdated: - ReleaseBuffer(buffer); - if (IsolationUsesXactSnapshot()) - ereport(ERROR, - (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), - errmsg("could not serialize access due to concurrent update"))); - if (ItemPointerIndicatesMovedPartitions(&hufd.ctid)) - ereport(ERROR, - (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), - errmsg("tuple to be locked was already moved to another partition due to concurrent update"))); - - /* Should not encounter speculative tuple on recheck */ - Assert(!HeapTupleHeaderIsSpeculative(tuple.t_data)); - if (!ItemPointerEquals(&hufd.ctid, &tuple.t_self)) - { - /* it was updated, so look at the updated version */ - tuple.t_self = hufd.ctid; - /* updated row should have xmin matching this xmax */ - priorXmax = hufd.xmax; - continue; - } - /* tuple was deleted, so give up */ - return false; - - case HeapTupleWouldBlock: - ReleaseBuffer(buffer); - return false; - - case HeapTupleInvisible: - elog(ERROR, "attempted to lock invisible tuple"); - break; - - default: - ReleaseBuffer(buffer); - elog(ERROR, "unrecognized heap_lock_tuple status: %u", - test); - return false; /* keep compiler quiet */ - } - - /* - * We got tuple - store it for use by the recheck query. - */ - ExecStorePinnedBufferHeapTuple(&tuple, slot, buffer); - ExecMaterializeSlot(slot); - break; - } - - /* - * If the referenced slot was actually empty, the latest version of - * the row must have been deleted, so we need do nothing. - */ - if (tuple.t_data == NULL) - { - ReleaseBuffer(buffer); - return false; - } - - /* - * As above, if xmin isn't what we're expecting, do nothing. - */ - if (!TransactionIdEquals(HeapTupleHeaderGetXmin(tuple.t_data), - priorXmax)) - { - ReleaseBuffer(buffer); - return false; - } - - /* - * If we get here, the tuple was found but failed SnapshotDirty. - * Assuming the xmin is either a committed xact or our own xact (as it - * certainly should be if we're trying to modify the tuple), this must - * mean that the row was updated or deleted by either a committed xact - * or our own xact. If it was deleted, we can ignore it; if it was - * updated then chain up to the next version and repeat the whole - * process. - * - * As above, it should be safe to examine xmax and t_ctid without the - * buffer content lock, because they can't be changing. - */ - - /* check whether next version would be in a different partition */ - if (HeapTupleHeaderIndicatesMovedPartitions(tuple.t_data)) - ereport(ERROR, - (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), - errmsg("tuple to be locked was already moved to another partition due to concurrent update"))); - - /* check whether tuple has been deleted */ - if (ItemPointerEquals(&tuple.t_self, &tuple.t_data->t_ctid)) - { - /* deleted, so forget about it */ - ReleaseBuffer(buffer); - return false; - } - - /* updated, so look at the updated row */ - tuple.t_self = tuple.t_data->t_ctid; - /* updated row should have xmin matching this xmax */ - priorXmax = HeapTupleHeaderGetUpdateXid(tuple.t_data); - ReleaseBuffer(buffer); - /* loop back to fetch next in chain */ - } - - /* signal success */ - return true; -} - -/* * EvalPlanQualInit -- initialize during creation of a plan state node * that might need to invoke EPQ processing. * @@ -2911,7 +2654,7 @@ EvalPlanQualFetchRowMarks(EPQState *epqstate) tuple.t_self = *((ItemPointer) DatumGetPointer(datum)); if (!heap_fetch(erm->relation, SnapshotAny, &tuple, &buffer, - false, NULL)) + NULL)) elog(ERROR, "failed to fetch tuple for EvalPlanQual recheck"); /* successful, store tuple */ |